This invention relates to spherical powder particles and to the process for producing the particles which involves mechanically reducing the size of a starting material followed by high temperature processing to produce spherical particles. More particularly the high temperature process is a plasma process.
U.S. Pat. No. 3,909,241 to Cheney et al relates to free flowing powders which are produced by feeding agglomerates through a high temperature plasma reactor to cause at least partial melting of the particles and collecting the particles in a cooling chamber containing a protective gaseous atmosphere where the particles are solidified.
Spherical refractory metal powders such as tungsten, molybdenum, niobium, tantalum, rhenium, and their alloys are useful in applications requiring good thermal and electrical conductivity and/or endurance at high temperatures and/or abrasive environments. Parts such as filters, precision press and sinter parts, injection molded parts, and electrical/electronic components may be made from these powders.
Refractory metal powders are generally produced by the reduction of oxides or the salts to metal resulting in nonspherical powder. Refractory based alloy powders containing difficult-to-reduce elements such as chromium, silicon, aluminum, and vanadium must be made from processes resulting in a coarse, often non-spherical powder.
Therefore, a process for efficiently converting coarse, often non-spherical refractory metal based powder to spherical powder would be an advancement in the art.
In European Patent Application No. WO8402864 published Aug. 2, 1984, there is disclosed a process for making ultra-fine powder by directing a stream of molten droplets at a repellent surface whereby the droplets are broken up and repelled and thereafter solidified as described therein. While there is a tendency for spherical particles to be formed after rebounding, it is stated that the molten portion may form elliptical shaped or elongated particles with rounded ends.